1. Field of the Invention
The invention is generally related to the area of optical information recordable medium. More particularly, the present is related to method and systems for controlling the eccentricity of bonded multiple optical discs, wherein an example of the bonded multiple optical discs is double-sided or double layered DVDs.
2. The Background of Related Art
One of the most popular optical storage medium is DVD (Digital Versatile Disc). Technically, DVD is a relatively new generation of optical disc storage technology. It is much larger in data capacity and faster in reading than CD and can hold cinema-like video, better-than-CD audio, still photos, and computer data. DVD aims to encompass home entertainment, computers, and business information with a single digital format. It has replaced laserdisc, is well on the way to replacing videotape and video game cartridges, and could eventually replace audio CD and CD-ROM. DVD has widespread support from all major electronics companies, all major computer hardware companies, and all major movie and music studios. With this unprecedented support, DVD became the most successful storage device of all time in the history of optical storage technologies.
There are a number of parameters in terms of quality of an optical medium (e.g., a DVD). One of them is an eccentricity (ECC) that defines a disparity between a geometric center of a round disc and a center of a data track. The geometric center is a center of a circle representing a round disc while the center of a data track (or data center) is a reference center from which the data tracks circle from the inside of the disc to the outside. As the reading/writing speed of a disc and the data density thereon increase, as well as the time to locate a data track decreases, the ECC becomes considerably important in overall quality parameters of an optical medium.
A double-layered DVD is formed by bonding two disks, each being 0.6 mm thick and commonly referred to as L0 or L1 substrate or disk. When being played in a DVD player, a DVD is positioned with reference to the geometric center of L0. If the data center of L0 is not matched with the geometric center of L0, there is an ECC on L0. Likewise, if the data center of L0 is not matched with the geometric center of L1, there is an ECC on L1. Further if the geometric centers of L0 and L1 are not matched, the ECC on L0 or L1 could be accumulated. FIG. 1 illustrates an ECC referenced by S when the centers of the two disks L0 and L1 are not exactly matched.
In a traditional manufacturing process, L0 and L1 substrates are applied with a layer of glue in between. L0 and L1 substrates are then bonded on a bonding station under a UV curing means. A bonding structure used in a bonding station, as shown in FIG. 2, includes a shaft 200 and a tray 202. The shaft 200 has a diameter of 14.8 mm while the inner diameter of the two disks is 15 mm. As a result, there is a gap that could introduce the disparity when the two disks are boned together. Such a gap leads to the ECC and causes the quality issue of the final disc.
There is a need for techniques to control the processing of bonding at least two disks so as to minimize the ECC of a final disc formed by the at least two bonded disks.